1. Field of the Invention
This invention relates to an improved method and apparatus for providing a back seal on packaging material used in a form, fill, and seal machine. More particulary, the method and apparatus is based on the use of cohesive sealants striped onto the edges of a web forming the package and activated, without the use of external heat, by applying pressure to the sealed area.
2. Prior Art
Form, fill, and seal machines utilize a web of packaging material or film which is moved intermittently and formed into a package while product is packed therein before the package is sealed. Such machines are commercially available, and for a general description of their operation, see the description in expired U.S. Pat. No. 2,899,875 and commonly owned Application Ser. No. 098,961 filed Nov. 30, 1979.
One of the typical known means for providing a back or longitudinal seal in such packaging on the current intermittent motion form, fill, and seal package machines involves the external application of heat and thermally activated film sealants. For example, see the above cited art. The use of heat in sealing produces an inherent limitation on the speed of production because sufficient heat must be transferred through an insulating medium (the packaging film). The transmission of such heat has been a siginficant limitation on package production rates in such machines.
Also, utilizing currently known techniques of heat-sealing in form-and-fill machines, the resultant thermal seals are subject to slip and dwell zone differentials in strength, width, and continuity. In other words, thermal seals produced on the known vertical and intermittent form-and-fill machines, while satisfactory, could stand improvement.
Also, heat-sealing in the environment such as described, requires significant amounts of electrical energy, and is subject to heater and control failures.
Additionally, cohesives not requiring external heat for activation are known sealing items, including packages. However, these cohesives have been generally used with single-ply film with surface printing. They are typically used in horizontal machines and not for packaging loose salted snack products.